An on-orbit ultra-high resolution SAR system and its working method

Abstract

The present invention discloses a spaceborne ultra-high resolution SAR system and its working method. The system includes a signal processor, a frequency multiplier unit, a receiver, a synthetic network front end, a traveling wave tube amplifier group, a limiting low-noise amplifier, a magic T, a waveguide switch, a circulator, a waveguide load, and an umbrella antenna. The system is installed on an agile satellite platform and realizes large-angle scanning imaging of a target area by means of the maneuver of the platform. There are multiple working methods through the combination of signals output from different ports of the magic T. The present invention not only realizes ultra-high resolution imaging superior to centimeter-level resolution, but also has the advantages of flexible working mode and good reliability. Moreover, the system has a simple composition. Through centralized transmission and reception, the volume and weight of the product are reduced, and it has the advantages of light weight and small heat dissipation, reducing the engineering development cost and difficulty.

Description

Technical Field

[0001] The present invention belongs to the field of spaceborne synthetic aperture radar (SAR), and relates to a spaceborne ultra-high resolution SAR system and its working method. Background Art

[0002] At present, the rapid development of remote sensing applications has put forward higher and higher requirements for the resolution of spaceborne SAR. The resolution requirement has been improved from the decimeter level to the centimeter level. As the system resolution gradually increases, the system transceiver signal bandwidth also increases accordingly. Centimeter-level resolution requires the system bandwidth to exceed 4 GHz. There are mainly two types of spaceborne SAR systems: one is the SAR based on a phased array antenna; the other is the SAR based on a reflector antenna. When the bandwidth increases to the order of several GHz, the phased array antenna will face problems such as serious dispersion and inconsistent beam pointing in the full bandwidth, while the reflector antenna does not have these problems and is particularly suitable for application in high-resolution SAR. At present, the maximum bandwidth of the spaceborne SAR system in the world only reaches 1.2 GHz, and its corresponding resolution is about 0.3 m, which cannot meet the need of centimeter-level resolution. Therefore, there is an urgent need for a spaceborne ultra-high resolution SAR system and its working method. Summary of the Invention

[0003] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a spaceborne ultra-high resolution SAR system and its working method to solve the above-mentioned deficiencies existing in the prior art. The system realizes the generation of ultra-wideband signals through a frequency multiplication unit, uses a reflector antenna to transmit the signals and receive the ground echoes, and inside the receiver, a power divider and a filter are used to divide the ultra-wideband echoes into multiple medium and small bandwidth echoes and down-convert them to the intermediate frequency. Finally, multi-channel analog-to-digital conversion is completed at the signal processor to become data and frame output; the system can generate signals with a bandwidth exceeding 4 GHz, meeting the need of centimeter-level resolution.

[0004] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0005] A spaceborne ultra-high resolution SAR system includes: a signal processor, a frequency multiplication unit, a synthetic network front end, a traveling wave tube amplifier group, a magic T, a waveguide load, a waveguide switch, a circulator, an umbrella antenna, a frequency synthesizer, a limiting low-noise amplifier, and a receiver; wherein:

[0006] The signal processor is used to generate medium and small bandwidth intermediate frequency signals and send them to the frequency multiplication unit, and at the same time collect multiple intermediate frequency echoes output by the receiver, and then frame and output the collected data; the signal processor also receives external remote control to generate various control signals inside the system and returns telemetry signals;

[0007] The frequency multiplication unit is used to multiply the medium and small bandwidth intermediate frequency transmission signals to the required bandwidth range to meet the system resolution requirements;

[0008] The synthetic network front end can receive the RF signals output by the frequency doubling unit, divide the power and send them to four phase shifters for phase adjustment;

[0009] The traveling wave tube amplifier group includes four traveling wave tube amplifiers for completing the power amplification of RF signals;

[0010] Three magic Ts can complete the power combination of high-power RF signals by combining the different signal phases controlled by the phase shifters;

[0011] Three waveguide switches can complete the selective output of three high-power RF signals;

[0012] Three waveguide loads can absorb the leakage signals to ensure that the system has low electromagnetic leakage;

[0013] The circulator is used to send high-power transmission signals to the umbrella antenna and then send the echo received by the umbrella antenna to the limiter low-noise amplifier;

[0014] The umbrella antenna is used to complete the external radiation of high-power RF signals and the reception of ground echoes;

[0015] The frequency synthesizer is used to generate the clock required by the signal processor and the local oscillator signal required by the receiver;

[0016] The limiter low-noise amplifier is used to withstand high-power leakage signals to prevent them from affecting subsequent electronic devices and at the same time complete the amplification of low-power echo signals;

[0017] The receiver is used to divide the broadband echo signal into multiple paths, select the frequency band for each path through different filters, and then down-convert it to the required intermediate frequency and send it to the signal processor for acquisition.

[0018] The present invention further includes the following technical features:

[0019] Specifically, the umbrella antenna is installed outside the satellite cabin and jointly maneuvers with the satellite platform during the imaging process to achieve large-angle scanning imaging of the target area.

[0020] Specifically, the principle for selecting the number of power division paths inside the receiver is as follows: Let the result obtained by dividing the system RF signal bandwidth by the acquisition rate of the signal processor and then multiplying by 2.4 be M, and the number of power division paths N be the smallest integer greater than or equal to M.

[0021] Specifically, the three magic Ts are magic T1, magic T2, and magic T3, and the four ports of magic T1, magic T2, and magic T3 are respectively port 1, port 2, port 3, and port 4; the three waveguide switches are waveguide switch 1, waveguide switch 2, and waveguide switch 3, and the three waveguide loads are waveguide load 1, waveguide load 2, and waveguide load 3.

[0022] Specifically, the four phase shifters are phase shifter 1, phase shifter 2, phase shifter 3, and phase shifter 4; the four traveling wave tube amplifiers are traveling wave tube amplifier 1, traveling wave tube amplifier 2, traveling wave tube amplifier 3, and traveling wave tube amplifier 4.

[0023] Specifically, the system has three operating modes, and each operating mode corresponds to different settings, including different phase shifter settings, the number of operating traveling wave tube amplifiers, and waveguide switch settings; the working method flow under all operating modes is as follows:

[0024] The signal processor generates an intermediate frequency signal with a medium and small bandwidth, the frequency doubling unit completes the signal bandwidth expansion to generate a radio frequency signal with the required bandwidth, the front end of the synthesis network completes power splitting and phase shifting, the traveling wave tube amplifier group completes power amplification, the high-power signal is sent to the circulator through the selection of the magic T and the waveguide switch, reaches the umbrella antenna and is radiated out, the echo received by the umbrella antenna enters the limiting low-noise amplifier for amplification after passing through the circulator, the amplified echo uses a power splitter and a filter inside the receiver to divide the large-bandwidth echo into multiple medium and small-bandwidth echoes and down-convert them to the intermediate frequency, and finally completes multi-channel analog-to-digital conversion at the signal processor to become data and frame output.

[0025] For the working method of the spaceborne ultra-high resolution SAR system, in the first operating mode, the transmission power is 2 times the output power of the traveling wave tube amplifier; there are the following two setting methods for the phase shifter settings, the number of operating traveling wave tube amplifiers, and the waveguide switch settings:

[0026] Method 1: Traveling wave tube amplifier 1 and traveling wave tube amplifier 2 work, phase shifter 1 is set to 0°, and phase shifter 2 is set to 180°; traveling wave tube amplifier 3 and traveling wave tube amplifier 4 do not work; waveguide switch 1 is set so that the signal is connected from port 4 of magic T1 to waveguide switch 3, waveguide switch 2 is set so that the signal is connected from waveguide switch 3 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from waveguide switch 1 to the circulator; at this time, the high-power transmission signal is output from port 4 of magic T1, passes through waveguide switch 1 and waveguide switch 3, reaches the circulator, and finally is radiated out from the umbrella antenna;

[0027] Method 2: Traveling wave tube amplifier 1 and traveling wave tube amplifier 2 do not work; traveling wave tube amplifier 3 and traveling wave tube amplifier 4 work, phase shifter 3 is set to 0°, and phase shifter 4 is set to 180°; waveguide switch 1 is set so that the signal is connected from waveguide switch 3 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic T2 to waveguide switch 3, and waveguide switch 3 is set so that the signal is connected from waveguide switch 2 to the circulator; at this time, the high-power transmission signal is output from port 4 of magic T2, passes through waveguide switch 2 and waveguide switch 3, reaches the circulator, and finally is radiated out from the umbrella antenna.

[0028] Specifically, in the second operating mode, the transmit power is 4 times the output power of the traveling wave tube amplifier; the settings of the phase shifters, the number of operating traveling wave tube amplifiers, and the setting method of the waveguide switches are as follows:

[0029] The traveling wave tube amplifier 1, the traveling wave tube amplifier 2, the traveling wave tube amplifier 3, and the traveling wave tube amplifier 4 operate. The phase shifter 1 is set to 0°, the phase shifter 2 is set to 0°, the phase shifter 3 is set to 0°, and the phase shifter 4 is set to 0°. The waveguide switch 1 is set so that the signal is connected from port 4 of the magic T1 to the waveguide load 1, the waveguide switch 2 is set so that the signal is connected from port 4 of the magic T2 to the waveguide load 2, and the waveguide switch 3 is set so that the signal is connected from port 3 of the magic T3 to the circulator. At this time, the high-power transmitted signal is output from ports 3 of the magic T1 and the magic T2, synthesized by the magic T3, enters the waveguide switch 3 and the circulator, and finally radiates out from the umbrella antenna.

[0030] Specifically, in the third operating mode, the transmit power is 1 times the output power of the traveling wave tube amplifier; there are four corresponding setting methods for the settings of the phase shifters, the number of operating traveling wave tube amplifiers, and the waveguide switches:

[0031] Method 1: The traveling wave tube amplifier 1 and the traveling wave tube amplifier 3 operate. The phase shifter 1 is set to 0°, and the phase shifter 3 is set to 0°. The traveling wave tube amplifier 2 and the traveling wave tube amplifier 4 do not operate. The waveguide switch 1 is set so that the signal is connected from port 4 of the magic T1 to the waveguide load 1, the waveguide switch 2 is set so that the signal is connected from port 4 of the magic T2 to the waveguide load 2, and the waveguide switch 3 is set so that the signal is connected from port 3 of the magic T3 to the circulator. At this time, the high-power transmitted signal is output from port 3 of the magic T3, reaches the circulator after passing through the waveguide switch 3, and finally radiates out from the umbrella antenna;

[0032] Method 2: The traveling wave tube amplifier 1 and the traveling wave tube amplifier 4 operate. The phase shifter 1 is set to 0°, and the phase shifter 4 is set to 0°. The traveling wave tube amplifier 2 and the traveling wave tube amplifier 3 do not operate. The waveguide switch 1 is set so that the signal is connected from port 4 of the magic T1 to the waveguide load 1, the waveguide switch 2 is set so that the signal is connected from port 4 of the magic T2 to the waveguide load 2, and the waveguide switch 3 is set so that the signal is connected from port 3 of the magic T3 to the circulator. At this time, the high-power transmitted signal is output from port 3 of the magic T3, reaches the circulator after passing through the waveguide switch 3, and finally radiates out from the umbrella antenna;

[0033] Mode 3: Traveling wave tube amplifiers 2 and 3 are operating, phase shifter 2 is set to 0°, and phase shifter 3 is set to 0°; traveling wave tube amplifiers 1 and 4 are not operating; waveguide switch 1 is set such that the signal is connected from port 4 of magic-T 1 to waveguide load 1, waveguide switch 2 is set such that the signal is connected from port 4 of magic-T 2 to waveguide load 2, and waveguide switch 3 is set such that the signal is connected from port 3 of magic-T 3 to the circulator; at this time, the high-power transmission signal is output from port 3 of magic-T 3, reaches the circulator after passing through waveguide switch 3, and is finally radiated from the umbrella antenna;

[0034] Mode 4: Traveling wave tube amplifiers 2 and 4 are operating, phase shifter 2 is set to 0°, and phase shifter 4 is set to 0°; traveling wave tube amplifiers 1 and 3 are not operating; waveguide switch 1 is set such that the signal is connected from port 4 of magic-T 1 to waveguide load 1, waveguide switch 2 is set such that the signal is connected from port 4 of magic-T 2 to waveguide load 2, and waveguide switch 3 is set such that the signal is connected from port 3 of magic-T 3 to the circulator; at this time, the high-power transmission signal is output from port 3 of magic-T 3, reaches the circulator after passing through waveguide switch 3, and is finally radiated from the umbrella antenna.

[0035] Compared with the prior art, the present invention has the following technical effects:

[0036] The present invention generates and transmits an ultra-wideband RF signal with a bandwidth of several GHz through a signal processor, frequency multiplier unit, traveling wave tube amplifier, magic-T, circulator, and umbrella antenna, and receives an ultra-wideband echo signal with a bandwidth of several GHz through the umbrella antenna, circulator, limiting low-noise amplifier, receiver, and signal processor, enabling centimeter-level resolution imaging and having the advantage of ultra-high resolution.

[0037] During the operation of the present invention, transmission signals with different powers can be generated by configuring the values of the phase shifters, the number of power amplifiers participating in the operation, and the states of the waveguide switches. The working mode is flexible and the reliability is good.

[0038] The present invention has a simple composition. Through centralized transmission and reception, the volume and weight of the product are reduced, having the advantages of light weight and low heat dissipation, and reducing the engineering development cost and difficulty. Description of the Drawings

[0039] Figure 1 is the block diagram of the spaceborne ultra-high resolution SAR system of the present invention.

[0040] Figure 2 is the high-power signal flow diagram of the first working mode setting method 1 of the present invention system.

[0041] Figure 3 is the high-power signal flow diagram of the first working mode setting method 2 of the present invention system.

[0042] Figure 4It is the high-power signal flow diagram of the second working mode setting method of the system of the present invention.

[0043] Figure 5 It is the high-power signal flow diagram of the first setting method of the third working mode of the system of the present invention.

[0044] Figure 6 It is the high-power signal flow diagram of the second setting method of the third working mode of the system of the present invention.

[0045] Figure 7 It is the high-power signal flow diagram of the third setting method of the third working mode of the system of the present invention.

[0046] Figure 8 It is the high-power signal flow diagram of the fourth setting method of the third working mode of the system of the present invention. Detailed implementation mode

[0047] The present invention provides a spaceborne ultra-high resolution SAR system, such as Figure 1 , including: a signal processor, a frequency multiplier unit, a synthetic network front end, a traveling wave tube amplifier group, a magic T, a waveguide load, a waveguide switch, a circulator, an umbrella antenna, a frequency synthesizer, a limiting low-noise amplifier, and a receiver; the signal processor transmits a medium and small bandwidth intermediate frequency signal, and then the frequency multiplier unit expands the signal bandwidth to the required bandwidth; the signal reaches the input port of the traveling wave tube amplifier after being power-divided and phase-shifted by the synthetic network front end; the traveling wave tube amplifier completes the power amplification of the radio frequency transmission signal, and its output signal enters the magic T to complete power synthesis; after the waveguide switch selects different high-power transmission signals, the transmission signal is sent to the circulator; the high-power transmission signal is transmitted from the umbrella antenna after passing through the circulator; after the radio frequency echo is received by the antenna, it reaches the limiting low-noise amplifier through the circulator, and after low-noise amplification, the radio frequency echo enters the receiver, is power-divided and filtered, and then down-converted to the received intermediate frequency, and finally the signal processor completes the echo data acquisition and packs and outputs it to the satellite platform. Among them, more specifically:

[0048] The signal processor is used to generate an intermediate frequency signal with a medium and small bandwidth and send it to the frequency multiplier unit, and at the same time collect multiple intermediate frequency echoes output by the receiver, and then frame and output the collected data; the signal processor also receives external remote control to generate various control signals inside the system and returns telemetry signals.

[0049] The frequency multiplier unit is used to multiply the intermediate frequency transmission signal with a medium and small bandwidth to the required bandwidth range to meet the resolution requirements of the system.

[0050] The synthetic network front end can receive the radio frequency signal output by the frequency multiplier unit, and after power division, it is sent to four phase shifters for phase adjustment.

[0051] The traveling wave tube amplifier group includes four traveling wave tube amplifiers and is used to complete the power amplification of radio frequency signals.

[0052] Three magic-Ts can complete the power combination of high-power RF signals by combining different signal phases controlled by phase shifters.

[0053] Three waveguide switches can complete the selective output of three high-power RF signals.

[0054] Three waveguide loads can absorb the leakage signals to ensure that the system has low electromagnetic leakage.

[0055] The circulator is used to send high-power transmission signals to the umbrella antenna and then send the echo received by the umbrella antenna to the limiter low-noise amplifier.

[0056] The umbrella antenna is used to complete the external radiation of high-power RF signals and the reception of ground echoes.

[0057] The frequency synthesizer is used to generate the clock required by the signal processor and the local oscillator signal required by the receiver.

[0058] The limiter low-noise amplifier is used to withstand high-power leakage signals to avoid affecting subsequent electronic devices and at the same time amplify small-power echo signals.

[0059] The receiver is used to divide the broadband echo signal into multiple paths. Each path selects a frequency band through a different filter and then down-converts it to the required intermediate frequency for acquisition by the signal processor.

[0060] Specifically, the umbrella antenna is installed outside the satellite cabin and jointly maneuvers with the satellite platform during the imaging process to achieve large-angle scanning imaging of the target area.

[0061] The principle for selecting the number of internal power splitting paths of the receiver is: Let the result obtained by dividing the system RF signal bandwidth by the acquisition rate of the signal processor and then multiplying by 2.4 be M, and the number of power splitting paths N be the smallest integer greater than or equal to M.

[0062] The three magic-Ts are magic-T1, magic-T2, and magic-T3. The four ports of magic-T1, magic-T2, and magic-T3 are respectively port 1, port 2, port 3, and port 4; the three waveguide switches are waveguide switch 1, waveguide switch 2, and waveguide switch 3, and the three waveguide loads are waveguide load 1, waveguide load 2, and waveguide load 3.

[0063] The four phase shifters are phase shifter 1, phase shifter 2, phase shifter 3, and phase shifter 4; the four traveling-wave tube amplifiers are traveling-wave tube amplifier 1, traveling-wave tube amplifier 2, traveling-wave tube amplifier 3, and traveling-wave tube amplifier 4.

[0064] The system of the present invention has three working modes. Each working mode corresponds to different settings, including phase shifter settings, the number of working traveling-wave tube amplifiers, and different waveguide switch settings; the working method flow under all working modes is:

[0065] The signal processor generates intermediate-frequency signals with medium and small bandwidths. The frequency multiplier unit completes the signal bandwidth expansion to generate radio-frequency signals with the required bandwidth. The front end of the synthesis network completes power splitting and phase shifting. The traveling-wave tube amplifier group completes power amplification. The high-power signal is sent to the circulator through the selection of magic-T and waveguide switches, and reaches the umbrella antenna for radiation. The echo received by the umbrella antenna enters the limiting low-noise amplifier for amplification after passing through the circulator. The amplified echo uses a power splitter and a filter inside the receiver to divide the large-bandwidth echo into multiple medium and small-bandwidth echoes and down-convert them to intermediate frequency. Finally, multi-channel analog-to-digital conversion is completed at the signal processor to become data and frame output.

[0066] In the first working mode, the transmit power is all 2 times the output power of the traveling-wave tube amplifier; there are the following two setting methods for the phase shifter setting, the number of working traveling-wave tube amplifiers, and the waveguide switch setting:

[0067] Method 1: Traveling-wave tube amplifier 1 and traveling-wave tube amplifier 2 work, phase shifter 1 is set to 0°, and phase shifter 2 is set to 180°; traveling-wave tube amplifier 3 and traveling-wave tube amplifier 4 do not work; waveguide switch 1 is set so that the signal is connected from port 4 of magic-T1 to waveguide switch 3, waveguide switch 2 is set so that the signal is connected from waveguide switch 3 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from waveguide switch 1 to the circulator; at this time, the high-power transmit signal is output from port 4 of magic-T1, passes through waveguide switch 1 and waveguide switch 3, and then reaches the circulator, and finally radiates out from the umbrella antenna; as Figure 2 shown.

[0068] Method 2: Traveling-wave tube amplifier 1 and traveling-wave tube amplifier 2 do not work; traveling-wave tube amplifier 3 and traveling-wave tube amplifier 4 work, phase shifter 3 is set to 0°, and phase shifter 4 is set to 180°; waveguide switch 1 is set so that the signal is connected from waveguide switch 3 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic-T2 to waveguide switch 3, and waveguide switch 3 is set so that the signal is connected from waveguide switch 2 to the circulator; at this time, the high-power transmit signal is output from port 4 of magic-T2, passes through waveguide switch 2 and waveguide switch 3, and then reaches the circulator, and finally radiates out from the umbrella antenna; as Figure 3 shown.

[0069] In the second working mode, the transmit power is 4 times the output power of the traveling-wave tube amplifier; the phase shifter setting, the number of working traveling-wave tube amplifiers, and the waveguide switch setting method:

[0070] The traveling-wave tube amplifiers 1, 2, 3, and 4 are operating. The phase shifter 1 is set to 0°, the phase shifter 2 is set to 0°, the phase shifter 3 is set to 0°, and the phase shifter 4 is set to 0°. The waveguide switch 1 is set such that the signal is connected from port 4 of the magic-T 1 to the waveguide load 1. The waveguide switch 2 is set such that the signal is connected from port 4 of the magic-T 2 to the waveguide load 2. The waveguide switch 3 is set such that the signal is connected from port 3 of the magic-T 3 to the circulator. At this time, the high-power transmission signal is output from ports 3 of the magic-T 1 and the magic-T 2, synthesized by the magic-T 3, enters the waveguide switch 3 and the circulator, and finally radiates out from the umbrella antenna; as Figure 4 shown.

[0071] In the third operating mode, the transmission power is 1 times the output power of the traveling-wave tube amplifier. There are four setting methods corresponding to the settings of the phase shifters, the number of operating traveling-wave tube amplifiers, and the waveguide switches:

[0072] Method 1: The traveling-wave tube amplifiers 1 and 3 are operating. The phase shifter 1 is set to 0°, and the phase shifter 3 is set to 0°. The traveling-wave tube amplifiers 2 and 4 are not operating. The waveguide switch 1 is set such that the signal is connected from port 4 of the magic-T 1 to the waveguide load 1. The waveguide switch 2 is set such that the signal is connected from port 4 of the magic-T 2 to the waveguide load 2. The waveguide switch 3 is set such that the signal is connected from port 3 of the magic-T 3 to the circulator. At this time, the high-power transmission signal is output from port 3 of the magic-T 3, reaches the circulator after passing through the waveguide switch 3, and finally radiates out from the umbrella antenna; as Figure 5 .

[0073] Method 2: The traveling-wave tube amplifiers 1 and 4 are operating. The phase shifter 1 is set to 0°, and the phase shifter 4 is set to 0°. The traveling-wave tube amplifiers 2 and 3 are not operating. The waveguide switch 1 is set such that the signal is connected from port 4 of the magic-T 1 to the waveguide load 1. The waveguide switch 2 is set such that the signal is connected from port 4 of the magic-T 2 to the waveguide load 2. The waveguide switch 3 is set such that the signal is connected from port 3 of the magic-T 3 to the circulator. At this time, the high-power transmission signal is output from port 3 of the magic-T 3, reaches the circulator after passing through the waveguide switch 3, and finally radiates out from the umbrella antenna; as Figure 6 shown.

[0074] Method 3: The traveling-wave tube amplifiers 2 and 3 are operating. The phase shifter 2 is set to 0°, and the phase shifter 3 is set to 0°. The traveling-wave tube amplifiers 1 and 4 are not operating. The waveguide switch 1 is set such that the signal is connected from port 4 of the magic-T 1 to the waveguide load 1. The waveguide switch 2 is set such that the signal is connected from port 4 of the magic-T 2 to the waveguide load 2. The waveguide switch 3 is set such that the signal is connected from port 3 of the magic-T 3 to the circulator. At this time, the high-power transmission signal is output from port 3 of the magic-T 3, reaches the circulator after passing through the waveguide switch 3, and finally radiates out from the umbrella antenna; as Figure 7 shown.

[0075] Mode 4: The traveling wave tube amplifier 2 and the traveling wave tube amplifier 4 are operating, the phase shifter 2 is set to 0°, and the phase shifter 4 is set to 0°; the traveling wave tube amplifier 1 and the traveling wave tube amplifier 3 are not operating; the waveguide switch 1 is set so that the signal is connected from port 4 of the magic T1 to the waveguide load 1, the waveguide switch 2 is set so that the signal is connected from port 4 of the magic T2 to the waveguide load 2, and the waveguide switch 3 is set so that the signal is connected from port 3 of the magic T3 to the circulator; at this time, the high-power transmission signal is output from port 3 of the magic T3, reaches the circulator after passing through the waveguide switch 3, and is finally radiated from the umbrella antenna; as Figure 8 shown.

[0076] The following gives specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0077] Embodiment:

[0078] This embodiment provides a spaceborne ultra-high resolution SAR system and its working method. Using the method of the present invention, a spaceborne SAR with a resolution of 7.5 cm is designed and operated. The system operates in the Ku band, with a working frequency range of 12.6 GHz to 17.4 GHz and a signal bandwidth of approximately 4.8 GHz. The specific implementation process is as follows:

[0079] The system is as Figure 1 shown, and includes: a signal processor, a frequency multiplier unit, a synthetic network front end, a traveling wave tube amplifier group, magic T1 - 3, waveguide loads 1 - 3, waveguide switches 1 - 3, a circulator, an umbrella antenna, a frequency synthesizer, a limiting low-noise amplifier, and a receiver.

[0080] The signal processor generates a medium-small bandwidth intermediate frequency signal with a frequency range of 2.1 GHz to 2.9 GHz and a bandwidth of 800 MHz and sends it to the frequency multiplier unit. At the same time, it acquires multiple intermediate frequency echo signals output by the receiver at a rate of 4 Gsps / channel, and then frames and outputs the acquired data; the signal processor also receives external remote control to generate various control signals inside the system and returns telemetry signals.

[0081] The frequency multiplier unit multiplies the medium-small bandwidth intermediate frequency signal with a frequency range of 2.1 GHz to 2.9 GHz and a bandwidth of 800 MHz by 6 times to the required working frequency range of 12.6 GHz to 17.4 GHz, which can meet the requirements of the system resolution.

[0082] The synthetic network front end receives the RF signal output by the frequency multiplier unit, divides the power, and sends it to 4 phase shifters for phase adjustment.

[0083] The traveling wave tube amplifier group consists of four traveling wave tube amplifiers to complete the power amplification of the RF signal.

[0084] Magic T 1 - 3 complete the power combination of high - power RF signals by combining the different signal phases controlled by the aforementioned phase shifters.

[0085] Waveguide switches 1 - 3 complete the selective output of three high - power RF signals.

[0086] Waveguide loads 1 - 3 absorb the leakage signals to ensure that the system has low electromagnetic leakage.

[0087] The circulator sends the high - power transmission signal to the umbrella antenna and then sends the echo received by the umbrella antenna to the limiter - low noise amplifier.

[0088] The umbrella antenna completes the external radiation of high - power RF signals and the reception of ground echoes.

[0089] The frequency synthesizer generates the clock required by the signal processor and the local oscillator signal required by the receiver.

[0090] The limiter - low noise amplifier withstands high - power leakage signals to prevent them from affecting subsequent electronic devices and at the same time amplifies the low - power echo signals.

[0091] The receiver divides the broadband echo signal into multiple paths. Each path selects a frequency band through a different filter and then down - converts to the required intermediate frequency and sends it to the signal processor for acquisition.

[0092] The umbrella antenna is installed outside the satellite cabin and jointly maneuvers and scans with the satellite platform during the imaging operation.

[0093] The principle for selecting the number of internal power - dividing paths of the receiver is as follows: The system RF signal bandwidth of 4.8 GHz divided by the signal processor acquisition rate of 4 Gsps and then multiplied by 2.4 gives a result of 2.88, and the number of power - dividing paths is 3.

[0094] In the second working mode setting method of the system, the phase shifter settings, the number of operating traveling - wave tube amplifiers, and the waveguide switch settings are as follows:

[0095] Traveling - wave tube amplifiers 1, 2, 3, and 4 operate. Phase shifter 1 is set to 0°, phase shifter 2 is set to 0°, phase shifter 3 is set to 0°, and phase shifter 4 is set to 0°; Waveguide switches 1 - 3 are set according to the Figure 4 shown state. At this time, the high - power transmission signal is output from ports 3 of Magic T1 and Magic T2, synthesized by Magic T3, enters waveguide switch 3 and the circulator, and finally radiates out from the umbrella antenna.

[0096] The above embodiments are only relatively preferred specific implementation manners of the present invention. The general changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0097] The content not described in detail in the specification of the present invention belongs to the well - known technology of those skilled in the art.

[0098] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0099] In addition, it should be noted that, in the case of no conflict, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0100] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A spaceborne ultra-high resolution SAR system, characterized in that: include: Signal processor, frequency multiplication unit, synthesis network front end, traveling wave tube amplifier group, magic T, waveguide load, waveguide switch, circulator, umbrella antenna, frequency synthesizer, limiting low noise amplifier and receiver; among which: The signal processor is used to generate intermediate frequency signals with small and medium bandwidths and send them to the frequency multiplication unit. At the same time, it collects the multi-channel intermediate frequency echoes output by the receiver, and then frames the collected data for output. The signal processor also receives external remote control to generate various control signals within the system and returns telemetry signals. The frequency multiplication unit is used to multiply the intermediate frequency transmission signal with small or medium bandwidth to the required bandwidth range to meet the system resolution requirements; The synthesis network front end can receive the RF signal output by the frequency multiplication unit and send it to four phase shifters for phase adjustment after power division; A traveling wave tube amplifier group, including four traveling wave tube amplifiers, is used to complete the power amplification of the radio frequency signal; Three magic Ts can combine the different signal phases controlled by the phase shifters to complete the power synthesis of high-power RF signals; Three waveguide switches can realize the selective output of three high-power RF signals; Three waveguide loads can absorb leakage signals and ensure the system has low electromagnetic leakage; Circulator, used to send high-power transmission signal to the umbrella antenna, and then send the echo received by the umbrella antenna to the limited low-noise amplifier; Umbrella antenna, used to radiate high-power radio frequency signals and receive ground echoes; Frequency synthesizer, used to generate the clock required by the signal processor and the local oscillator signal required by the receiver; Limiting low noise amplifier, used to withstand high-power leakage signals to prevent them from affecting subsequent electronic equipment, while completing the amplification of low-power echo signals; The receiver is used to divide the broadband echo signal into multiple paths. Each path selects the frequency band through a different filter, and then down-converts it to the required intermediate frequency and sends it to the signal processor for collection.

2. The spaceborne ultra-high resolution SAR system according to claim 1, characterized in that: The umbrella antenna is installed outside the satellite cabin and maneuvers in conjunction with the satellite platform during the imaging process to achieve large-angle scanning imaging of the target area.

3. The spaceborne ultra-high resolution SAR system according to claim 1, characterized in that: The principle for selecting the number of power splitters inside the receiver is as follows: assume that the system RF signal bandwidth is divided by the signal processor acquisition rate and then multiplied by 2.4 to obtain a result M, and the number of power splitters N is the smallest integer greater than or equal to M.

4. The spaceborne ultra-high resolution SAR system according to claim 1, characterized in that: The three magic Ts are magic T1, magic T2 and magic T3, and the four ports of magic T1, magic T2 and magic T3 are port 1, port 2, port 3 and port 4 respectively; the three waveguide switches are waveguide switch 1, waveguide switch 2 and waveguide switch 3, and the three waveguide loads are waveguide load 1, waveguide load 2 and waveguide load 3.

5. The spaceborne ultra-high resolution SAR system according to claim 4, characterized in that: The four phase shifters are phase shifter 1, phase shifter 2, phase shifter 3 and phase shifter 4; the four traveling wave tube amplifiers are traveling wave tube amplifier 1, traveling wave tube amplifier 2, traveling wave tube amplifier 3 and traveling wave tube amplifier 4.

6. The operating method of the spaceborne ultra-high resolution SAR system according to claim 5, characterized in that: The system has three working modes, each of which corresponds to different settings, including phase shifter settings, number of traveling wave tube amplifiers, and waveguide switch settings; the working method flow in all working modes is: The signal processor generates an intermediate frequency signal with a small or medium bandwidth, the frequency multiplication unit completes signal bandwidth expansion to generate a radio frequency signal with a required bandwidth, the synthesis network front end completes power division and phase shifting, the traveling wave tube amplifier group completes power amplification, and the high-power signal is sent to the circulator through the selection of the magic T and waveguide switch, reaches the umbrella antenna and radiates out, and the echo received by the umbrella antenna enters the limiting low-noise amplifier after passing through the circulator for amplification. The amplified echo is divided into a plurality of small or medium bandwidth echoes by a power divider and a filter inside the receiver, and down-converted to the intermediate frequency, and finally the multi-channel analog-to-digital conversion is completed at the signal processor to become data and output in a frame.

7. The operating method of the spaceborne ultra-high resolution SAR system according to claim 6, characterized in that: In the first working mode, the transmission power is 2 times the output power of the traveling wave tube amplifier; the phase shifter setting, the number of traveling wave tube amplifiers working, and the waveguide switch setting correspond to the following two setting methods: Mode 1: TWT amplifiers 1 and 2 are working, phase shifter 1 is set to 0°, and phase shifter 2 is set to 180°; TWT amplifiers 3 and 4 are not working; waveguide switch 1 is set so that the signal is connected from port 4 of magic T1 to waveguide switch 3, waveguide switch 2 is set so that the signal is connected from waveguide switch 3 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from waveguide switch 1 to circulator; at this time, the high-power transmission signal is output from port 4 of magic T1, passes through waveguide switch 1 and waveguide switch 3 to the circulator, and finally radiates from the umbrella antenna; Mode 2: TWT amplifier 1 and TWT amplifier 2 do not work; TWT amplifier 3 and TWT amplifier 4 work, phase shifter 3 is set to 0°, and phase shifter 4 is set to 180°; waveguide switch 1 is set so that the signal is connected from waveguide switch 3 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic T2 to waveguide switch 3, and waveguide switch 3 is set so that the signal is connected from waveguide switch 2 to the circulator; at this time, the high-power transmission signal is output from port 4 of magic T2, reaches the circulator after passing through waveguide switch 2 and waveguide switch 3, and finally radiates from the umbrella antenna.

8. The operating method of the spaceborne ultra-high resolution SAR system according to claim 6, characterized in that: In the second working mode, the transmission power is 4 times the output power of the traveling wave tube amplifier; the phase shifter setting, the number of traveling wave tube amplifiers working, and the waveguide switch setting method are: Traveling wave tube amplifier 1, traveling wave tube amplifier 2, traveling wave tube amplifier 3, and traveling wave tube amplifier 4 are working, phase shifter 1 is set to 0°, phase shifter 2 is set to 0°, phase shifter 3 is set to 0°, and phase shifter 4 is set to 0°; waveguide switch 1 is set so that the signal is connected to waveguide load 1 from port 4 of magic T1, waveguide switch 2 is set so that the signal is connected to waveguide load 2 from port 4 of magic T2, and waveguide switch 3 is set so that the signal is connected to the circulator from port 3 of magic T3; at this time, the high-power transmission signal is output from port 3 of magic T1 and magic T2, and after being synthesized by magic T3, it enters waveguide switch 3 and circulator, and finally radiates from the umbrella antenna.

9. The operating method of the spaceborne ultra-high resolution SAR system according to claim 6, characterized in that: In the third working mode, the transmission power is 1 times the output power of the traveling wave tube amplifier; there are four corresponding settings for the phase shifter setting, the number of traveling wave tube amplifiers working, and the waveguide switch setting: Mode 1: Traveling wave tube amplifier 1 and traveling wave tube amplifier 3 are working, phase shifter 1 is set to 0°, and phase shifter 3 is set to 0°; traveling wave tube amplifier 2 and traveling wave tube amplifier 4 are not working; waveguide switch 1 is set so that the signal is connected from port 4 of magic T1 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic T2 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from port 3 of magic T3 to circulator; at this time, the high-power transmission signal is output from port 3 of magic T3, reaches the circulator after passing through waveguide switch 3, and finally radiates from the umbrella antenna; Mode 2: Traveling wave tube amplifier 1 and traveling wave tube amplifier 4 are working, phase shifter 1 is set to 0°, phase shifter 4 is set to 0°; traveling wave tube amplifier 2 and traveling wave tube amplifier 3 are not working; waveguide switch 1 is set so that the signal is connected from port 4 of magic T1 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic T2 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from port 3 of magic T3 to circulator; at this time, the high-power transmission signal is output from port 3 of magic T3, reaches the circulator after passing through waveguide switch 3, and finally radiates from the umbrella antenna; Mode 3: TWT amplifier 2 and TWT amplifier 3 are working, phase shifter 2 is set to 0°, and phase shifter 3 is set to 0°; TWT amplifier 1 and TWT amplifier 4 are not working; waveguide switch 1 is set so that the signal is connected from port 4 of magic T1 to waveguide load 1, waveguide switch 2 is set so that the signal is connected from port 4 of magic T2 to waveguide load 2, and waveguide switch 3 is set so that the signal is connected from port 3 of magic T3 to circulator; at this time, the high-power transmission signal is output from port 3 of magic T3, reaches the circulator after passing through waveguide switch 3, and finally radiates from the umbrella antenna; Mode 4: TWT amplifier 2 and TWT amplifier 4 are working, phase shifter 2 is set to 0°, and phase shifter 4 is set to 0°; TWT amplifier 1 and TWT amplifier 3 are not working; waveguide switch 1 is set so that the signal is connected to waveguide load 1 from port 4 of magic T1, waveguide switch 2 is set so that the signal is connected to waveguide load 2 from port 4 of magic T2, and waveguide switch 3 is set so that the signal is connected to the circulator from port 3 of magic T3; at this time, the high-power transmission signal is output from port 3 of magic T3, reaches the circulator after passing through waveguide switch 3, and finally radiates from the umbrella antenna.

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